CSS2 style fix using a CSS trick and wrapper with class .aspect-ratio:

.aspect-ratio {
position: relative;
width:100%;
height:0;
padding-bottom:56%;/* The height of the item will now be 56% of the width. */}/* Adjust the iframe so it's rendered in the outer-width and outer-height of it's parent */.aspect-ratio iframe {
position: absolute;
width:100%;
height:100%;
left:0;
top:0;}